Our views on antibody formation underwent recently a revolution initiated by the work of Tonegawa in Basel, (Switzerland) who found that the genes of antibody forming lymphoid cells of animal embryos undergo a drastic rearrangement of their genome. For many years it had been assumed that all the entire DNA molecules are transcribed into mRNA molecules, and that the tri-nucleotides of mRNA are precisely translated into amino acid residues of the newly formed proteins. New methods for the determination of nucleotide sequences in DNA and RNA revealed that the conversion of DNA into RNA involves fragmentation of large portions of the DNA molecules, elimination of some of the fragments and recombination of the other fragments. These discoveries are difficult to reconcile with the widely accepted assumption that the role of the antigen merely stimulation of cells containing preformed antibody molecules. In the present paper we investigate antibody molecules produced by the administration of azoproteins which contain determinant hapten groups of the general structure -N double bond N double bond C6H4-X where C6H4 is the benzene ring of an azo-benzene residue and X is one of the following residues; p-SO3H, p-AsO3H2, m-SO3H, or p-COOH. We have prepared antibodies directed against each of these four groups and are testing now the mutual cross-reactivity of the four antigenic determinants with the four types of antibody. We hope to find out in this way whether the specificity of the antibodies produced is genetically predetermined or whether it is determined by interaction of the antigen molecules with the recombining RNA fragments, orienting them in such a way that the final product, the antibody molecules, is complementarily adjusted to the administered antigenic determinant.